For iOS 3.0 and above, you just have to call :
- (void)reloadRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation;
To reload row 3 of section 2 and row 4 of section 3 for example, you'll have to do this :
// Build the two index paths
NSIndexPath* indexPath1 = [NSIndexPath indexPathForRow:3 inSection:2];
NSIndexPath* indexPath2 = [NSIndexPath indexPathForRow:4 inSection:3];
// Add them in an index path array
NSArray* indexArray = [NSArray arrayWithObjects:indexPath1, indexPath2, nil];
// Launch reload for the two index path
[self.tableView reloadRowsAtIndexPaths:indexArray withRowAnimation:UITableViewRowAnimationFade];